Apparatus for sensing of chlorine dioxide

ABSTRACT

The instant invention provides apparatuses for measuring the level or concentration of chlorine dioxide gas in a sample and methods of using the same. One aspect of the invention provides an apparatus for measuring a concentration of a chlorine dioxide gas in a sample. The apparatus includes a light emitting diode (LED), a light sensor, and a flow path between the LED and the light sensor, and a filter configured to remove chlorine dioxide from a reference stream. The flow path is capable of containing a sample. The sensor is capable of measuring the level of chlorine dioxide in the sample and the reference stream.

RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2009/049924, filed Jul. 8, 2009, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/134,245, filed Jul. 8, 2008.The entire contents of the aforementioned applications are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods and apparatuses for the sensingand delivery of chlorine dioxide, e.g., gaseous chlorine dioxide.

BACKGROUND OF THE INVENTION

Chlorine dioxide was discovered in the early 1800's, and was adopted bycommerce in the United States in the 1940's. Chlorine dioxide has beencalled the ideal biocide and the ability of chlorine dioxide to reduceor eliminate viable microbes, e.g., bacteria, viruses, fungi, moldspores, algae and protozoa, is well-documented and well known. See, forexample, Franklin, C. L. et al. (1991) Am Vet Med Assoc 198:1625-30;Korich K. G., et al. (1990) Appl Environ Microbiol. 56:1423-8; Boddie etal. (2000) J Dairy Sci. 83:2975-9; Lee et al. (2004) J Food Prot.67:1371-6; Han et al. (2003) J Environ Health 66:16-21; Sy et al. (2005)J Food Prot. 68:1176-87; and LeChevallier M. W. et al. (1988) ApplEnviron Microbiol. 54:2492-9.

Chlorine dioxide inactivates microorganisms by oxidizing key componentsof a micro-organism's membrane proteins that are vital to the membrane'sstructure and function. Also, the oxidizing reaction that causesmicroorganism inactivation does not form trihalomethanes (THMs) orhaloacetic acids (HAAs).

Approvals and registrations for use of chlorine dioxide in a widevariety of applications have been granted by the EPA, FDA and USDA, andsuch approvals and registrations have led to an increasing adoption ofthe use of chlorine dioxide.

There are many reasons for the ongoing expansion of chlorine dioxide useincluding its effectiveness against microorganisms.

Accordingly, with the increased use of chlorine dioxide the need existsfor sensing chlorine dioxide concentration in a sample to determine andto validate efficacy of performance with a proscribed concentration ofchlorine dioxide and/or to determine when a treated environment is safe.

SUMMARY OF THE INVENTION

The instant invention provides apparatus and methods for sensing theamount or levels of chlorine dioxide gas in a sample.

In one embodiment, the invention provides apparatuses for measuring aconcentration of a chlorine dioxide gas in a sample, comprising a lightemitting diode (LED), a light sensor, and a flow path between the LEDand the light sensor, the flow path capable of containing a sample,wherein the sensor is capable of measuring the level of chlorine dioxidein a sample and a reference measurement.

In one embodiment, the apparatus further comprises one or more filters,wherein the filters are used to remove the chlorine dioxide gas from asample to obtain the reference measurement.

In another embodiment, the apparatus further comprises a second LED,light sensor and flow path for determining the reference measurement.

In a specific embodiment, the sample is obtained from a location thathas not been treated with chlorine dioxide, i.e., when determining thelevel in a reference measurement.

In another embodiment, the sample is not measured until the referencemeasurement is less than about 10 ppm chlorine dioxide.

In another embodiment, the sensor and/or LED is thermostated. In anotherembodiment, the sensor is heated, for example, to prevent condensation.

In another embodiment, the LED generates a narrow wavelength band. In aspecific embodiment, the wavelength band is narrower than the absorbanceband of chlorine dioxide. In a specific embodiment, the narrowwavelength band is in the UV, for example near an absorption peak ofchlorine dioxide.

In one embodiment, the light sensor is a photodiode. In a specificembodiment, the photodiode sensitivity is matched to the LED. In oneembodiment, the apparatus further comprises a filter to select awavelength of light matched to the LED.

In another embodiment, the apparatus further comprises an air movingdevice, e.g., a fan or a pump.

In one embodiment, the apparatus further comprises an inlet and anoutlet port for the target sample. In one embodiment, the filter is atthe inlet. In a specific embodiment, the filter is an activated carbonfilter.

In another embodiment, the filter further comprises a filter at theoutlet. In one embodiment, the filter is suitable for filtering acids orhydrogen chloride gas.

In exemplary embodiments, the path lengths are 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12 or more inches in length.

In another embodiment, the light attenuation is less than 10%.

In another embodiment, the path between the sensor and the detectorincludes one or more mirrors. In a specific embodiment, the one or moremirrors are curved. In another embodiment, the mirrors are for focusingthe light source on the light sensor. In a specific embodiment, themirrors are mirrors are moveable.

In another embodiment, the apparatuses further comprise two or morepaths used for sensing different concentration levels or for referencemeasurements.

In another embodiment, the apparatuses further comprise one or morelenses for focusing the light on the detector.

In another embodiment, the apparatuses further comprise one or moresignal amplifiers.

In another embodiment, the apparatuses further comprise a recorder orindicator, e.g., a recorder or indicator having a wireless connection toa recorder or display.

In one embodiment, the apparatus further comprises a chlorine dioxidegenerating apparatus.

In another embodiment, the invention provides apparatuses for measuringa concentration of a chlorine dioxide gas in a sample, comprising afirst sensor for measuring the level of chlorine dioxide gas in asample, and a second sensor for measuring the level of chlorine dioxidegas in a sample; wherein each sensor comprises: a light emitting diode(LED), a light sensor, and a flow path between the LED and the lightsensor, the flow path capable of containing a sample, and wherein thesecond sensor measures the levels of chlorine dioxide gas in sampleafter the first sensor determines that the level of chlorine dioxide gasin a sample is less than about 15 ppm; and wherein second sensor alsomeasures a reference measurement.

In one embodiment, the second sensor further comprises one or morefilters to remove chlorine dioxide gas from a sample prior to measuringthe reference measurement.

In another embodiment, the sample is obtained from a location that hasnot been treated with chlorine dioxide.

In another embodiment, the sensors and/or LEDs are thermostated. Inanother embodiment, the sensors are heated, for example, to preventcondensation.

In another embodiment, the LEDs generate a narrow wavelength band. In aspecific embodiment, the wavelength band is narrower than the absorbanceband of chlorine dioxide. In a specific embodiment, the narrowwavelength band is in the UV, for example near an absorption peak ofchlorine dioxide.

In one embodiment, the light sensor is a photodiode. In a specificembodiment, the photodiode sensitivity is matched to the LED. In oneembodiment, the apparatus further comprises a filter to select awavelength of light matched to the LED.

In another embodiment, the apparatus further comprises an air movingdevice, e.g., a fan or a pump.

In one embodiment, the apparatus further comprises an inlet and anoutlet port for the target sample. In one embodiment, the filter is atthe inlet. In a specific embodiment, the filter is an activated carbonfilter.

In another embodiment, the filter further comprises a filter at theoutlet. In one embodiment, the filter is suitable for filtering acids orhydrogen chloride gas.

In exemplary embodiments, the path lengths are 1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12 or more inches in length.

In another embodiment, the light attenuation is less than 10%.

In another embodiment, the path between the sensor and the detectorincludes one or more mirrors. In a specific embodiment, the one or moremirrors are curved. In another embodiment, the mirrors are for focusingthe light source on the light sensor. In a specific embodiment, themirrors are mirrors are moveable.

In another embodiment, the apparatuses further comprise two or morepaths used for sensing different concentration levels or for referencemeasurements.

In another embodiment, the apparatuses further comprise one or morelenses for focusing the light on the detector.

The invention also provides methods for determining the amount of levelof chlorine dioxide gas in a sample using the chlorine dioxide sensorapparatuses described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a chlorine dioxide sensor apparatus of the invention.

FIG. 2 depicts a chlorine dioxide sensor apparatus comprising a filterand an air moving device.

FIG. 3 depicts a chlorine dioxide sensor apparatus with two pathlengths.

FIG. 4 a depicts a chlorine dioxide sensor apparatus with a lens.

FIG. 4 b depicts the chlorine dioxide sensor apparatus as in FIG. 4 afurther comprising gas tight seals.

FIG. 5 depicts a chlorine dioxide sensor apparatus comprising areference cell.

FIG. 6 depicts a chlorine dioxide sensor apparatus as part of a chlorinedioxide gas generator.

FIG. 7 is a schematic of an amplification circuit for a chlorine dioxidesensor apparatus.

FIGS. 8A-B are pictures of a chlorine dioxide sensor apparatus of theinvention.

FIG. 9 is a curve of chlorine dioxide sensor apparatus data from adecontamination run in a controlled environment.

FIG. 10 depicts a compilation of extinction coefficients for ClO₂ atroom temperature.

FIG. 11 depicts an exemplary spectrum from a 360 nm LED taken from theFoxUV™ 360 nm LED 5 mm.

DETAILED DESCRIPTION

The instant invention provides methods and apparatus for measuring theamount or concentration of chlorine dioxide gas in a sample. In specificembodiments, the apparatus also obtains a reference measurement of theamount or concentration of chlorine dioxide gas in a reference sample.

In reference to FIG. 1, the invention provides a chlorine dioxide sensorapparatus 1, comprising inlet 4, outlet 5, and light emitting diode(LED) 2 separated from photodetector 3 by flow path 6. Flow path 6 is ofsufficient volume to contain a sample of gas, e.g., gas comprisingchlorine dioxide gas. In one embodiment of the invention LED 2 is set upopposite a photodiode 3 so that the sample flows between the LED and thephotodiode.

In reference to FIG. 2, in certain embodiments, the invention provides achlorine dioxide sensor apparatus as in FIG. 1, and further comprisingfilter 7, air moving device 9 and valve 12. Valve 12 functions tocontrol the location that the sample is collected from prior to entryinto flow path 6. Air moving device 9 assists in moving the samplethrough flow path 6. In exemplary embodiments, air moving device 9 is afan.

FIG. 3 depicts an alternative geometry of the chlorine dioxide sensorapparatus wherein apparatus comprises a beam splitter 13. Thisembodiment comprises two photodetectors 3 and a geometry such that aportion of the light from LED 2 is directed to photodetector 3 a and aportion is directed to photodetector 3 b.

FIG. 4 depicts an additional element of chlorine dioxide sensorapparatus 1. Specifically, FIG. 4 depicts lens 10 a and lens 10 b placedin path length 6 proximal to LED 2 and photodetector 3, respectively.FIG. 4 b further depicts gas tight seals 14 around lens 10 a and 10 b.

FIG. 5 depicts an embodiment of the invention wherein apparatus 1comprises two LEDs 2, photodetectors 3, and flow paths 6. In oneembodiment, the first flow path 6 a is used to measure a sample of airfrom an environment treated with chlorine dioxide gas. In oneembodiment, this first flow path 6 a is used to measure chlorine dioxidegas until the level reaches a level of at least below about 20 ppm, 15ppm, 10 ppm or 5 ppm. At such time where the level is below thisconcentration, the second flow path 6 b is used to accurately determinethe level of chlorine dioxide in a sample. In one embodiment, the secondflow path 6 b is capable of collecting a reference measurement and asample measurement to accurately determine the amount or concentrationof chlorine dioxide gas in a sample. The reference measurement can becollected by first filtering a sample to remove chlorine dioxide gasusing, for example, an activated charcoal filter, or can be collected bymeasuring a sample that was not treated by chlorine dioxide.

In one embodiment of the apparatus depicted in FIG. 5, the two flowpaths 6 a, 6 b are different lengths. In an exemplary embodiment, thefirst path length (used to measure the higher concentrations) is shorterthan the second path length.

FIG. 6 depicts chlorine dioxide sensor apparatus 1 attached to chlorinedioxide generator 11.

FIG. 7 depicts an exemplary a schematic of an amplification circuit fora chlorine dioxide sensor apparatus.

FIGS. 8A-B depicts pictures of a prototype chlorine dioxide sensorapparatus of the invention.

FIG. 9 is a curve of chlorine dioxide sensor apparatus data from adecontamination run in a controlled environment demonstrating thefunctionality of the instrument as set forth in the examples.

FIG. 10 depicts a compilation of extinction coefficients for ClO₂ atroom temperature and FIG. 11 depicts an exemplary emission spectrum froma 360 nm LED taken from a FoxUV™ LED having a 5 mm diameter and a 360 nmwavelength.

Exemplary photodetectors can be, for example, ThorLabs part numberFDS100 Si Photodiode.

Chlorine dioxide has a specific absorption spectra which limits thelight reaching the photodiode. The absorption spectrum of chlorinedioxide consists of a various peaks and the wavelength of thephotodetector, i.e., photodiode, should be set to match a lightabsorbing spectral region of the sample. For example, low-costcommercially available 360 nm or 420 nm LEDs are preferred LEDs forchlorine dioxide. An exemplary LED used in the chlorine dioxide sensorapparatuses described herein can be, for example, Fox Group part numberFG360-R5-WC015. The sensor will typically be in a light baffledenclosure that prevents stray light from affecting the measurement. TheLED is preferably also in the enclosure. The enclosure will typicallyhave an inlet and an outlet for the ClO₂ containing sample stream. Oftenthe electronics and sensitive optics will be isolated from the ClO₂containing fluid stream. If necessary, flow path isolation can beaccomplished with hydrochloric acid resistant materials. If the fluid isgaseous, maintaining the critical components at a slightly elevatedtemperature will prevent condensation and often provide sufficientprotection from corrosion. Accordingly, in specific embodiments of theinvention, the apparatus comprises a thermostat and heating and/orcooling equipment to regulate the temperature of the apparatus so as toavoid condensation and/or maintain a stable operating temperature of theLED.

Selection of photodetectors that have a larger band gap can reduce thesensitivity to stray light at wavelengths longer than the energycorresponding to the band gap. An example of such a photodetector is theGaN UV enhanced diode PDU-G105A manufactured by Advanced Photonics Inc.

In a preferred embodiment, the LED 2 is driven with a current source toreduce sensor variation due to temperature and other variation becausephoton production in an LED is primarily proportional to current.

In a preferred embodiment, the photodiode uses a current sensing circuitto reduce sensor variation due to temperature, voltage and othervariation. A voltage sensing circuit may be used, but the sensed voltagewill not be linear with illumination level.

In another preferred embodiment, a reference photodiode can be used toeither feedback stabilize the LED output, or to normalize the responseof the sensing photodiode. Taking the ratio of the sensed total currentto the reference photodiode current is a typical way to normalize theoutput.

In a preferred embodiment a fan or pump will be used to move a samplechlorine dioxide gas through the flow path between the light source 2and the sensor 3.

When exposed to high energy photons (UV light, for example) chlorinedioxide in the presence of humidity can decompose and form hydrochloricacid. In a preferred embodiment, the components of the apparatus arearranged so the sample flow exits any hydrochloric acid from the sensorwithout passing any corrosion sensitive components.

In certain embodiments of the invention, a filter 7 is used to scrub thechlorine dioxide gas from a sample in order to obtain a referencemeasurement. In one embodiment, the filter 7 is an activated charcoalfilter.

In another embodiment, an additional filter 15, such as a HEPA filterimpregnated with sodium bicarbonate, is placed at the outlet 5 toneutralize any hydrogen chloride formed.

The path length between the LED 2 and the photodetector 3 will determinethe absorption with a relatively long path length, such as 12 inches,used to sense lower concentrations and relatively short path length,such as 3 inches, to sense higher concentrations.

In one embodiment of the invention, one or more mirrors are used tocreate a long path length within a relatively small sensor enclosure byreflecting the light from the light source one or more times before thelight reaches the detector. The multiple pass folded optical path isused to increase the sensitivity. The following folded optical pathdesigns are incorporated into this document by reference: Multiple passoptical cells are used to achieve very long optical path lengths in asmall volume and have been extensively used for absorption spectroscopy,(White, J. U., “Long Optical Paths of Large Aperture,” J. Opt. Soc. Am.,vol. 32, pp 285-288 (May 1942); Altmann, J. R. et al., “Two-mirrormultipass absorption cell,” Appl. Opt., vol. 20, No. 6, pp 995-999 (15Mar. 1981) laser delay lines (Herriott, D. R., et al., “Folded OpticalDelay Lines,” Appl. Opt., vol. 4, No. 8, pp 883-889 (August 1965)),Raman gain cells (Trutna, W. R., et al., “Multiple-pass Raman gaincell,” Appl. Opt., vol. 19, No. 2, pp 301-312 (15 Jan. 1980)),interferometers (Herriott, D. H., et al., “Off-Axis Paths in SphericalMinor Interferometers,” Appl. Opt., vol. 3, No. 4, pp 523-526 (April1964)), photoacoustic spectroscopy (Sigrist M. W., et al., “Laserspectroscopic sensing of air pollutants,” Proc. SPIE, vol. 4063, pp. 17(2000)) and other resonators (Yariv, A., “The Propagation of Rays andSpherical Waves,” from Introduction to Optical Electronics, Holt,Reinhart, and Winston, Inc., New York (1971), Chap. 2, pp 18-29; Salour,M. M., “Multipass optical cavities for laser spectroscopy,” Laser Focus,50-55 (October 1977)). Cells have taken the form of White cells (White,J. U., “Long Optical Paths of Large Aperture,” J. Opt. Soc. Am., vol.32, pp 285-288 (May 1942)) and its variants (Chernin, S. M. andBarskaya. E. G., “Optical multipass matrix systems,” Appl. Opt., vol.30, No. 1, pp 51-58 (January 1991)), integrating spheres (Abdullin, R.M. et al., “Use of an integrating sphere as a multiple pass opticalcell,” Sov. J. Opt. Technol., vol. 55, No. 3, pp 139-141 (March 1988)),and stable resonator cavities (Yariv, A., “The Propagation of Rays andSpherical Waves,” from Introduction to Optical Electronics, Holt,Reinhart, and Winston, Inc., New York (1971)).

The stable resonator is typified by the design of Herriott (Herriott, D.H., et al., “Off-Axis Paths in Spherical Minor Interferometers,” Appl.Opt., vol. 3, No. 4, pp 523-526 (April 1964)). The simplest suchHerriott cell consists of two spherical mirrors of equal focal lengthsseparated by a distance d less than or equal to four times the focallengths f of the mirrors. This corresponds to stable resonatorconditions. A collimated or focused laser beam is injected through thecenter of a hole in one of the mirrors, typically an off-axis locationnear the mirror edge. The beam is periodically reflected and refocusedbetween these mirrors and then exits through the center of the inputhole (corresponding exactly to the entry position of the input beam,defining the re-entrant condition) after a designated number of passesN, in a direction (slope) that is different from the entry slope. As aresult, the total optical path traversed in the cell is approximatelyNd. The pattern of reflected spots observed on the mirrors in thesecells forms an ellipse. Re-entrant conditions for spherical mirrorHerriott cells are restricted by certain predetermined ratios of themirror separation d to the focal length f and the location and slope ofthe input beam. For any re-entrant number of passes N, all allowedsolutions are characterized by a single integer M. Excellentdescriptions for the design, setup and use of these cells are given byAltmann (Altmann, J. R., et al., “Two-mirror multipass absorption cell,”Appl. Opt., vol. 20, No. 6, pp 995-999 (15 Mar. 1981) and McManus(McManus, J. B., et al., “Narrow optical interference fringes forcertain setup conditions in multipass absorption cells of the Herriotttype,” Appl. Opt., vol. 29, No. 7, pp 898-900 (1 Mar. 1990)).

When the cell volume must be minimized relative to the optical pathlength or where a very long optical path (>50 m) or very small footprintis desired, it is useful to increase the density of passes per unitvolume of cell. The conventional spherical mirror Herriott cell islimited by the number of spots one can fit along the path of the ellipsewithout the spot adjacent to the output hole being clipped by or exitingthat hole at a pass number less than N. This approximately restricts thetotal number of passes to the circumference of the ellipse divided bythe hole diameter, which in turn is limited by the laser beam diameter.For a 25-mm radius mirror with a relatively small 3-mm diameter inputhole located 20 mm from the center of the mirror, a maximum of about

${\frac{2{\pi 20}}{3} \approx 40},$

or 80 passes is possible at best. Generally, the hole is made larger toprevent any clipping of the laser input beam that might lead toundesirable interference fringes, and typical spherical Herriott cellsemploy less than 60 passes.

Herriott (Herriott, D. R. and Schulte, H. J., “Folded Optical DelayLines,” Appl. Opt., vol. 4, No. 8, pp 883-889 (August 1965))demonstrated that the use of a pair of astigmatic mirrors could greatlyincrease the spot density, and hence optical path length, in the cell.Each mirror has different finite focal lengths (f_(x) and f_(y)) alongorthogonal x and y axes, and the mirrors are aligned with the same focallengths parallel to one another. The resulting spots of each reflectionon the mirrors create precessions of ellipses to form Lissajouspatterns. Since these patterns are distributed about the entire face ofeach mirror, many more spots can be accommodated as compared to a cellwith spherical mirrors. Herriott defines the method of creating theastigmatic mirror as distortion of a spherical mirror, either inmanufacture or in use, by squeezing a spherical mirror in its mount. Hestates that the amount of astigmatism required is very small and amountsto only a few wavelengths. McManus (McManus, et al., “Astigmatic mirrormultipass absorption cells for Ion-path-length spectroscopy,” Appl.Opt., vol. 34, No. 18, pp 3336-3348 (20 Jun. 1995)) outlines the theoryand behavior of this astigmatic Herriott cell and shows that the densityof passes can be increased by factors of three or more over sphericalmirror cells. For these astigmatic mirror cells, light is injectedthrough a hole in the center of the input mirror. Allowed solutions forre-entrant configurations are characterized by a pair of integer indicesM_(x) and M_(y), since there are now two focal lengths present alongorthogonal axes.

Chlorine dioxide has a UV extinction coefficient which varies rapidlywith wavelength as depicted in FIG. 10. Beers Law states that therelationship between light attenuation and concentration will belogarithmic. Beers Law is applicable only to absorbance over bandwidthssufficiently narrow to contain essentially a single extinctioncoefficient. In one embodiment of the invention using a light sourcewhich covers a wavelength range that is broad compared to the extinctioncoefficient fine structure, the light level and path length are set tohave a small percentage loss of light so the light attenuation is nearlylinearly proportional to the sample concentration. The path length ischosen to preferably contain less than 50%, more preferably less than30%, and still more preferably less than 10% extinction of light at thepeak absorbance wavelength incorporated in the measurement.

In another embodiment of the invention, using multiples optical passes,the number of passes is changed during the measurement to vary the pathlength. The absorbance is calculated from at least two different pathlengths according to Beers law and the divergence from Beers law is usedto determine the level of ClO₂. Adsorption and scattering losses due tomirror surface contamination as well as scattering losses from thesample stream are broad spectrum and will be relatively wavelengthindependent over any portion of the wavelength range between 300 to 440nanometers, and therefore will adhere to Beers law. The light loss fromthe spectral fine structure of the extinction coefficient will notfollow Beers law, but is calculated by integrating the Beers law resultfor each narrow bandwidth slice of the spectrum using the specific lightintensities and the corresponding extinction coefficients. See FIG. 11for a typical light intensity vs. wavelength for a suitable LED.

In another embodiment of the invention, one or more curved mirrors areused to focus the light on the detector.

In another embodiment of the invention, lenses are used to focus thelight source on the detector to get a larger signal from the sample.

In another embodiment of the invention, a reference signal is used.

In another embodiment of the invention, the sensor is run without asample at the beginning of each use cycle to determine a referencesignal.

In another embodiment of the invention, one or more path lengths areused simultaneously. In this way, low concentrations, such as 0.1 to 0.3ppm, can be measured accurately as well as high concentrations, such as500-2000 ppm, in the same sensor. Typically there is a large rangebetween decontamination concentrations and safe gas levels, so it isuseful to measure both low levels for safety and high levels for dosing.

In a further embodiment of the invention, the short path signal may beused as a reference signal for low concentrations. At highconcentrations, the short path signal is used with the reference signalbeing saved from before introduction of the ClO2. In another embodimentof the invention the sensor electronics uses two gain stages to measurehigh and low concentrations of the sample.

In another embodiment, a movable mirror is used to vary the path lengthfrom short to long with a single light source and sensor. Comparison ofthe two signals from the short and long path lengths can be used to makea sensor with two accurate ranges that are several orders of magnitudeapart.

In another embodiment of the invention, the sensor output is recorded,for example by a digital data acquisition system, for later review. Theoutput may include other relevant information such as the test date,decontamination protocol, equipment code, temperature, humidity, etc.

In another embodiment of the sensor, the sample stream is repeatedlyalternated with a reference stream that is free of the ClO₂. Thiscompensates for optical surface contamination as well as light sourceand detector changes that may take place over the monitoring time. Inone version of this embodiment, the reference stream is derived from thesample stream by passing the sample stream through a scrubbing filter 7,such as activated carbon, preferably with a high surface area.

In another embodiment of the sensor alternating a sample stream with areference stream, a ClO₂ scrubber such as an activated carbon filter isplaced on the exhaust of the sensor. The reference stream is obtained byreversing the direction of flow through the sensor, so the stream passesthrough the scrubber before entering the sensor.

In another embodiment of the sensor alternating a sample stream with areference stream, the reference stream is obtained from a sourceindependent of the ClO₂ treatment zone. A specific embodiment related tomeasurement and control of ClO₂ levels inside an enclosed treatmentspace such as a bio-safety cabinet, the reference gas stream is obtainedfrom outside the treatment space.

In another embodiment of the invention the sensor include wirelesscommunication to a recorder or readout. Being able to place sensorsthroughout an environment to be decontaminated is desirable. Forexample, placing a sensor above the HEPA filter in a biosafety cabinetwill allow confirmation that the required dose of disinfectant wasdelivered in a hard to reach location.

The instant invention provides apparatus and methods for sensing anddelivering chlorine dioxide.

In one embodiment of the invention, a chlorine dioxide generator isplaced inside a controlled environment to be decontaminated.

In one embodiment of the invention, a chlorine dioxide generator isconnected to a controlled environment through one or more ports.

In one embodiment of the invention, a chlorine dioxide generator isconnected to a controlled environment through in inlet and outlet port.

In another embodiment of the invention, the chlorine dioxide generatorhas a sensor.

In another embodiment of the invention, the sensor feeds backinformation about the chlorine dioxide concentration and adjusts theoutput of the generator to control the dose profile, concentration vs.time, for the decontamination.

In another embodiment of the invention, a pressure sensor is used tocheck the controlled environment for leak rate either at the beginningof the process or continuously during the process.

In another embodiment, a pump or fan is used to maintain the controlledenvironment at a negative pressure so chlorine dioxide does not escapethe controlled environment. In another embodiment the flow rate passingthrough this pump or fan, as well as the differential pressure ismonitored.

In another embodiment, a filter 15, for example an activated carbonfilter, is used at the outlet to adsorb some of the chlorine dioxideexiting the controlled environment.

In another embodiment, a filter 15, for example an activated carbonfilter, is used at the outlet to adsorb some of the chlorine dioxideexiting the controlled environment so the exiting flow is below a safetylimit (0.3 or 0.1 ppm, for example) for chlorine dioxide.

In another embodiment, a humidity and temperature sensor is used toensure that water vapor is not condensing inside the controlledenvironment.

In another embodiment, a humidification means is used to control thehumidity in the controlled environment. High humidity, for example70-95% RH, has been shown to increase bacterial spores' susceptibilityto chlorine dioxide.

In another embodiment, a dehumidification means is used remove liquidwater from the controlled environment.

In another embodiment, two or more sensors are used as a safety check.

In another embodiment, two or more sensors are used where the sensorsare place to measure concentration in different parts of the controlledenvironment to measure the dose to that area.

The various combinations of the above embodiments are intended to bewithin the scope of the instant invention.

Example 1

Chlorine dioxide gas was generated by a chlorine dioxide generator and asensor apparatus of the invention was used to measure the concentrationof chlorine dioxide in the treated environment. The results of thisexperiment are presented in FIG. 9.

INCORPORATION BY REFERENCE

The contents of all references, patents, pending patent applications andpublished patents, cited throughout this application are herebyexpressly incorporated by reference.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the instant invention and the followingclaims.

1. An apparatus for measuring a concentration of a chlorine dioxide gasin a sample, the apparatus comprising, a light emitting diode (LED), alight sensor, and a flow path between the LED and the light sensor, theflow path capable of containing a sample; and a filter configured toremove chlorine dioxide from a reference stream; wherein the sensor iscapable of measuring the level of chlorine dioxide in the sample and thereference stream.
 2. The apparatus of claim 1, further comprising asecond light sensor.
 3. The apparatus of claim 1, wherein the sensor andthe LED are thermostated.
 4. The apparatus of claim 1, wherein theapparatus is heated.
 5. The apparatus of claim 1, further comprising anair moving device.
 6. The apparatus of claim 1, wherein the filter is anactivated carbon filter.
 7. The apparatus of claim 1, further comprisinga second filter at the outlet.
 8. The apparatus of claim 7, wherein thesecond filter is suitable for neutralizing acids.
 9. The apparatus ofclaim 7, wherein the second filter is suitable for neutralizing hydrogenchloride gas.
 10. The apparatus of claim 1, wherein the path between thesensor and the detector includes one or more optical elements forfocusing the light source on the light sensor.
 11. The apparatus ofclaim 10, wherein the optical elements include one or more lenses forfocusing the light on the detector.
 12. The apparatus of claim 1,further comprising two or more optical paths within the flow path, theoptical paths used for sensing different concentration levels or forreference measurements.
 13. The apparatus of claim 1, further comprisinga wireless connection to a recorder or display.
 14. The apparatus ofclaim 1, further comprising a chlorine dioxide generating apparatus. 15.The apparatus of claim 1, further comprising a valve configured toalternatively admit the sample or the reference stream into the flowpath.
 16. The apparatus of claim 1, wherein the reference stream isobtained from the same source as the sample.
 17. An apparatus formeasuring a concentration of a chlorine dioxide gas in a sample,comprising: a first chlorine dioxide sensor for measuring the level ofchlorine dioxide gas in a sample, and a second chlorine dioxide sensorfor measuring the level of chlorine dioxide gas in a sample; whereineach chlorine dioxide sensor comprises: a light emitting diode (LED), alight sensor, and a flow path between the LED and the light sensor, theflow path capable of containing the sample; and wherein the secondchlorine dioxide sensor measures the levels of chlorine dioxide gas inthe sample after the first chlorine dioxide sensor determines that thelevel of chlorine dioxide gas in the sample is less than about 15 ppm;and wherein second chlorine dioxide sensor also measures a referencemeasurement.
 18. The apparatus of claim 17, wherein the second chlorinedioxide sensor further comprises one or more filters to remove chlorinedioxide gas from the sample prior to measuring the referencemeasurement.
 19. An apparatus for measuring a concentration of achlorine dioxide gas in a sample, the apparatus comprising: a lightemitting diode (LED); a first light sensor; a second light sensor; and abeam splitter configured to direct a first portion of light from the LEDto the first light sensor and a second portion of light from the LED tothe second light sensor, such that a first path traveled by the firstportion of light has a different length than a second path traveled bythe second portion of light.
 20. The apparatus of claim 19, furthercomprising: a filter configured to remove chlorine dioxide from thesample to generate a reference stream.